臺灣博碩士論文加值系統

Indium nitride (InN) with a narrow direct band gap has superior electronic transport properties over other group-III nitrides and it makes InN attractive for applications such as high-frequency electronic devices, near-infrared optoelectronics, and high-efficiency solar cells. With the rapid down-sizing of electronic and photonic device dimensions, understanding of the carrier transportation in nanoscale materials becomes crucial. In this thesis, we report the ultrafast carrier dynamics of vertically aligned InN nanorod arrays grown by molecular-beam epitaxy on Si (111) substrates. We employ ultrafast optical spectroscopy at a wide range of probe wavelengths (800 nm – 1600 nm) to understand the absorption/relaxation process of nanorods with different rod height, diameter, and rod density. The band-filling effect dominant absorption process is observed for nanorods, while the band-gap renormalization effect is dominant in epilayer. Typically, band-gap renormalization is significant in high carrier density and then band-filling dominant absorption in InN nanorods indicates smaller carrier density than in epilayer, due to less efficient absorption limited by the size of nanorods. Polarization-dependent transient reflectivity responses in nanorods shows that carrier lifetimes along parallel and perpendicular directions to the axis of nanorods are different only for small-diameter nanorods, implying that the carrier confinement can occur in the nanorods with the diameter comparable to theirs diffusion length.

Indium nitride (InN) with a narrow direct band gap has superior electronic transport properties over other group-III nitrides and it makes InN attractive for applications such as high-frequency electronic devices, near-infrared optoelectronics, and high-efficiency solar cells. With the rapid down-sizing of electronic and photonic device dimensions, understanding of the carrier transportation in nanoscale materials becomes crucial. In this thesis, we report the ultrafast carrier dynamics of vertically aligned InN nanorod arrays grown by molecular-beam epitaxy on Si (111) substrates. We employ ultrafast optical spectroscopy at a wide range of probe wavelengths (800 nm – 1600 nm) to understand the absorption/relaxation process of nanorods with different rod height, diameter, and rod density. The band-filling effect dominant absorption process is observed for nanorods, while the band-gap renormalization effect is dominant in epilayer. Typically, band-gap renormalization is significant in high carrier density and then band-filling dominant absorption in InN nanorods indicates smaller carrier density than in epilayer, due to less efficient absorption limited by the size of nanorods. Polarization-dependent transient reflectivity responses in nanorods shows that carrier lifetimes along parallel and perpendicular directions to the axis of nanorods are different only for small-diameter nanorods, implying that the carrier confinement can occur in the nanorods with the diameter comparable to theirs diffusion length.

Abstract..…. I
Acknowledgrnment..…. Ⅱ
Chapter1 Introduction 1
1-1 Properties of InN film and InN nanorods 2
1-2 Femtosecond pump probe technique 4
1-3 Thesis structure 5
Chapter2 Carrier dynamics in semiconductor 6
2-1 Effects of carrier generation 8
2-2.1 Band-filling effect 8
2-2.2 Band-gap renormalization 10
2-2.3 Free carrier absorption 11
2-2 Scattering processes in ultrafast regime 12
2-2.1 Carrier-carrier scattering 12
2-2.2 Carrier-phonon scattering 13
2-3 Effects of carrier recombination 14
2-3.1 Radiative recombination 15
2-3.2 Nonradiative recombination 16
2-3.3 Auger recombination 17
Chapter3 Experimental and sample 18
3-1 Transient photo-reflection pump-probe measurement 18
3-2 Optical parametric amplifiers 20
3.3 Experimental system of reflection pump probe setup 22
3-4 Sample preparation 24
3-4.1 InN film 24
3-4.2 InN nanorod 26

Chapter4 Results and discussions 33
4-1 InN film 33
4-2 InN nanorods 37
4-2.1 Wavelength dependent 37
4-2.2 Pump fluence dependent 46
4-2.3 Polarization state dependent 51

Chapter5 Conclusion 55
Reference 56

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